In conventional electromagnetic relays, when a moveable contact moves away from a fixed contact, an electric arc is often generated across the contacts. The resulting heat melts the contacts to a certain extent, and this substantially reduces the service life of the electromagnetic relay. In some cases, the contacts may be welded together by this heat, thereby rendering the electromagnetic relay totally unusable.
An electromagnetic relay typically consists of a casing, an electromagnet unit received in the casing and including an electromagnetic coil, and a contact unit which is also received in the casing and actuated by the electromagnet unit. In small relays, the casing is so small that the coil leads of the electromagnetic coil and the terminal pieces of the contact unit are required to be arranged undesirably close together. When the exposed parts of the coil leads and the terminal pieces are arranged close together, it become increasingly difficult to ensure a sufficient insulation therebetween over the entire service life of the electromagnetic relay.